Synthetic and natural ester based lubricants are used in a large number of applications including, for example, automotive and aviation oils, refrigeration oils, metal working fluids, gear oils, turbo oils, hydraulic fluids and refrigeration lubricants.
Synthetic and natural ester based lubricants, however, are well known to be very sensitive to the effects of water. Hydrolysis of such lubricants can substantially shorten the lubricant life and lead to a higher risk of equipment failure. Further, it is known in the art that inclusion of anti-wear additives in ester base oils can accelerate the hydrolytic degradation of esters due to their acidic nature. Thus, at least one common additive exacerbates the hydrolytic instability of ester base oils.
Several approaches have been taken to increase the hydrolytic stability of ester based lubricants. In one approach, additives, such as dicarbo-imides, are included in various amounts to minimize ester hydrolysis. In another approach, esters having a significant level of steric hindrance around the ester functionality have been used to minimize ester hydrolysis. Neither approach has satisfactorily solved the problem ester based lubricant hydrolytic stability.